Austenitic alloys for turbochargers

Abstract

The present disclosure relates to a novel iron-based austenitic alloy for a turbocharger housing and to methods of its preparation.

The invention claimed is: 
     
       1. A turbocharger housing for an internal combustion engine comprising an iron-based austenitic alloy, wherein the iron-based austenitic alloy consists of the following composition:
 C: 0.3 to 0.45 wt. %, 
 Cr: 20 to 22 wt. %, 
 Mn: 9.5 to 11.5 wt. %, 
 Ni: 3 to 4 wt. %, 
 Si: 1.2 to 2.1 wt. %, 
 Nb: 0.4 to 0.6 wt. %, 
 V: 0.3 to 0.6 wt. %, 
 Mo: 0.3 to 0.6 wt. %, 
 N: 0.1 to 0.35 wt. %; 
 impurities in a total amount of less than 3 wt. %; and 
 Fe as balance; 
 wherein the turbocharger housing is cast from the iron-based austenitic alloy and wherein the iron-based austenitic alloy has a melting temperature of less than 1550° C. 
 
     
     
       2. The turbocharger housing according to  claim 1 , wherein the iron-based austenitic alloy has a melting temperature in the range of 1450° C. to less than 1550° C. 
     
     
       3. The turbocharger housing according to  claim 1 , wherein the iron-based austenitic alloy has less than 4% sigma phases. 
     
     
       4. The turbocharger housing according to  claim 1 , wherein the iron-based austenitic alloy has less than 2% sigma phases. 
     
     
       5. The turbocharger housing according to  claim 1 , wherein the microstructure of the iron-based austenitic alloy has an average grain size of between 2 and 4, measured according to ASTM E112-12. 
     
     
       6. The turbocharger housing according to  claim 1 , wherein an inner surface of the turbocharger housing that is in contact with exhaust gas or compressed air has a surface roughness Rz of less than 100. 
     
     
       7. A process for preparing a turbocharger housing as defined in  claim 1 , comprising
 a) melt mixing elements of the following composition, wherein the composition consists of: 
 C: 0.3 to 0.45 wt. %, 
 Cr: 20 to 22 wt. %, 
 Mn: 9.5 to 11.5 wt. %, 
 Ni: 3 to 4 wt. %, 
 Si: 1.2 to 2.1 wt. %, 
 Nb: 0.4 to 0.6 wt. %, 
 V: 0.3 to 0.6 wt. %, 
 Mo: 0.3 to 0.6 wt. %; 
 N: 0.1 to 0.35 wt. %; 
 impurities in a total amount of less than 3 wt. %; and 
 Fe as balance, to form an iron-based austenitic alloy melt; 
 b) casting the melt into a turbocharger housing. 
 
     
     
       8. The process according to  claim 7 , wherein the turbocharger housing is subjected to thermal aging at 1000° C. to 1060° C. for at least 1 hour, followed by cooling at a rate of up to 80° C./h. 
     
     
       9. The process according to  claim 7 , wherein casting is an investment casting or a sand casting process.